This invention relates to slide fasteners, more particularly to a slider-operated fastener of the concealed or masked type which in its closed disposition substantially simulates a garment seam.
Slide fasteners having two rows of interlocking fastener elements formed from a continuous filament or wire and secured to respective folded edges of opposed stringer tapes are well known, and such fasteners when closed by the slider mask the elements from external view, only leaving a linear seam in the junction of the opposed tapes.
The so-called "Concealed" slide fasteners of known type are designed to maintain the effect of concealing or masking the fastener elements by folding the respective element-carrying edges of stringer tapes on themselves about the sewn seam which secures the respective row of fastener elements to the tape and which extends longitudinally of the tape and outermost of the elements or close to the coupling heads thereof. Such known concealed type slide fasteners include stringer tapes of a warp-knitted structure having on one surface alternate longitudinal wales and inter-wale grooves, with fastener elements mounted on the other relatively flat surface along the respective longitudinal edges of the tapes which are folded. When attaching such a fastener to a garment or the like, it is necessary to unfold and erect the respective folded edges with the coupling heads of the fastener elements directed towards the plane of the garment and thereafter to sew the respective stringer tapes precisely along the longitudinal inter-wale grooves closest to the coupling heads of the elements. However, when the respective element-carrying edges of the tapes are thus erected substantially in an L-shaped fashion, the wales located on opposite sides of the inter-wale groove through which the sewing threads are to extend are urged toward each other, causing that particular inter-wale groove to be narrowed or otherwise crushed in a manner illustrated in FIG. 3 of the accompanying drawings, with the results that the sewing needle is liable to damage in contact with adjacent wales or to be mis-guided into other adjacent grooves away from the fastener elements. This has often led to mal-functioning of the concealed fastener.